This invention relates to a process for the ecological reclamation of industrial working fluids and/or outdoor working locations such as those encountered in oil and gas well exploration. The present invention is particularly useful for the clarification of oil and gas well working fluids and drilling pit solidification and reclamation.
Oil or gas well exploration typically includes on site generation of various waste products which are instant to the drilling and exploration process. Drilling pits are usually excavated for use by the operator to assist in the well completion phase of the exploration and are usually found close to the drilling site. There is typically more than one pit used in the drilling operation. The number of pits and the type of discharge into the pit will vary depending upon the nature of the drilling operation. Typically, separate pits are used to contain working fluids including drilling fluid and fracture or return fluid from the formation fracture.
The working fluids have a fresh or saltwater base stock and contain soluble and insoluble contaminants which may be dispersed or colloidally suspended. Insoluble contaminants together with entrapped fluid tend to collect as a layer of sludge several feet deep along the bottom of the pit. In addition to naturally occurring contaminants, artificial contaminants may include chemicals used in the drilling process to aid well stimulation, assist the drilling fluid to carry the drill cuttings out of the hole and protect fresh water zones and the integrity of the hole itself.
Naturally occurring contaminants in the working fluid or pit water comprise silt formed of loose soil, clay, sand, rock and other earthen debris and include indigenous soluble salts such as calcium, sodium and potassium chlorides and iron which is typically present in both ferrous and ferric states. Artificial contaminants are generally chemical additives which include, for example, cationic clay stabilizers, anionic drilling soaps, nonionic surfactants, drilling gels, corrosion inhibitors and bactericides.
The pH of the working fluid or pit water is usually within the range of 4 to 7. On standing, some of the ferrous iron commonly found in the "frac" water returned from the formation and held in the pit is air oxidized to ferric iron in this pH range. The ferric iron precipitates as ferric hydroxide and results in the pit having a rusty red-brown color. The remaining ferrous iron remains in solution. Heavy metals such as barium, lead, cadmium and zinc may also be present in the pit waters.
The drilling permit holder has the responsibility for cleaning up the pit site area in accordance with applicable local and EPA requirements. Pursuant to these requirements, the drilling permit holder must return the site to an ecologically acceptable condition. In the past, the driller tended to separately deal with the clarification of the pit water and the reclamation of the pit area.
In removing the pit water, the driller may dispose of it by either incurring the expense of transporting the water in the pit to a properly licensed disposal site or pumping it into an injection well, e.g. an exhausted oil or gas well. In the latter case, the pit water is first filtered to eliminate solids such as the above-mentioned ferric hydroxide or sand to avoid plugging the well. During this process, it is known that the iron in the ferrous state often interacts with entrained air and becomes oxidized to the ferric state which results in precipitation in the hole and possible plugging and/or the need for expensive clean-up treatment.
In addition to the above reinjection process, the prior art discloses processes for treating particular contaminants present in oil and gas well brines. U.S. Pat. No. 4,465,598 teaches the precipitation of metals including iron, nickel, chromium, cobalt and manganese from oil and gas well heavy brines which have been filtered initially to remove solids. A suitable oxidizing agent is added to the brine to oxidize the metals to an oxidation state of +3 or higher for precipitation as oxides. The pH of the brine may be raised to allow oxide formation by addition of basic substances including alkali metal hydroxides and alkaline earth metal hydroxides including calcium hydroxide. U.S. Pat. No. 4,634,533 teaches an oil and gas well brine treatment including an initial oxidizing treatment to convert iron to the ferric state.
In addition to the treatment and removal of water from the pit, it is necessary to clean and fill the pit in an ecologically suitable manner. The sludge and working fluid remaning in the pit was heretofore distributed within a plurality of subsequently excavated "laterals" comprising narrow channels into which the sludge and remaining fluid was flowed and/or pushed. The laterals have humped bottoms which form separate collection traps for the fluid and sludge. Thereafter, the topsoil excavated in forming the pit and laterals is back-filled. Thus, the prior art pit clean-up processmerely diluted the sludge/working fluid over a larger area provided by the laterals and involved considerable additional excavation costs.
It is also known in the art to use various types of lime for sludge clean-up. U.S. Pat. No. 4,079,003 teaches a process of initially draining the pit water and then applying calcium oxide to solidify the resultant sludge and raise the pH to at least 12.4. The exothermic lime reaction is indicated to convert the sludge into a solid reaction product which is effective to confine the toxic materials. The pH of the sludge is subsequently reduced by addition of acid.